Rhodium(II)-catalyzed inter- and intramolecular enantioselective cyclopropanations with alkyl-diazo(triorganylsilyl)acetates

Article abstract of DOI:10.1002/hlca.200490256

The intermolecular cyclopropanation of styrene with ethyl diazo(triethylsilyl)acetate (1a) proceeds at room temperature in the presence of chiral Rh^II carboxylate catalysts derived from imide-protected amino acids and affords mixtures of trans- and cis-cyclopropane derivatives 2a in up to 72% yield but with modest enantioselectivities (< 54%) (Scheme 1 and Table 1). Protiodesilylation of a diastereoisomer mixture 2a with Bu₄NF is accompanied by epimerization at C(1) (→ 3). The intramolecular cyclopropanation of allyl diazo(triethylsilyl)acetate (8a), in turn, affords optically active 3-oxabicyclo[3.1.0]hexan-2-one (9a) with yields of up to 85% and 56% ee (Scheme 3 and Table 2). Similarly, the (2Z)-pent-2-enyl derivative 8d reacts to 9d in up to 77% yield and 38% ee (Scheme 3 and Table 3). In contrast, the diazo decomposition of (2E)-3-phenylprop-2-enyl and 2-methylprop-2-en-1-yl diazo(triethyl-silyl)acetates (8b and 8c, resp.) is unsatisfactory and gives very poor yields of substituted 3-oxabicyclo[3.1.0]hexan-2-ones 9b and 9c, respectively (Table 3).

Full text of DOI:10.1002/hlca.200490256

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Helvetica Chimica Acta Vol. 87 (2004)
Rhodium(II)-Catalyzed Inter- and Intramolecular Enantioselective
Cyclopropanations with Alkyl-Diazo(triorganylsilyl)acetates
Paul M¸ller*, and Fabienne Lacrampe
Department of Organic Chemistry, University of Geneva, 30, Quai Ernest Ansermet, CH-1211 Geneva 4
(phone: ‡ 41223796527; fax: ‡ 41223793215; e-mail: paul.muller@chiorg.unige.ch)
The intermolecular cyclopropanation of styrene with ethyl diazo(triethylsilyl)acetate (1a) proceeds at room
temperature in the presence of chiral RhII carboxylate catalysts derived from imide-protected amino acids and
affords mixtures of trans- and cis-cyclopropane derivatives 2a in up to 72% yield but with modest
enantioselectivities (< 54%) (Scheme 1 and Table 1). Protiodesilylation of a diastereoisomer mixture 2a with
Bu4NF is accompanied by epimerization at C(1) ( ! 3). The intramolecular cyclopropanation of allyl
diazo(triethylsilyl)acetate (8a), in turn, affords optically active 3-oxabicyclo[3.1.0]hexan-2-one (9a) with yields
of up to 85% and 56% ee (Scheme 3 and Table 2). Similarly, the (2Z)-pent-2-enyl derivative 8d reacts to 9d in up
to 77% yield and 38% ee (Scheme 3 and Table 3). In contrast, the diazo decomposition of (2E)-3-phenylprop-2-
enyl and 2-methylprop-2-en-1-yl diazo(triethyl-silyl)acetates (8b and 8c, resp.) is unsatisfactory and gives very
poor yields of substituted 3-oxabicyclo[3.1.0]hexan-2-ones 9b and 9c, respectively (Table 3).
1. Introduction. The photochemical decomposition of diazo(trialkylsilyl)methyl
ketones in the absence of reagents affords products derived from either Wolff
rearrangement or 1,2-alkyl migration of the intermediate carbenes [1]. In the presence
of olefins, these carbenes are trapped, and cyclopropanes with high stereospecificity
may be isolated [2]. The transition-metal-catalyzed decomposition of alkyl diazo-
(trialkylsilyl)acetates in the presence of styrene (ˆethenylbenzene) and hex-1-ene has
been investigated by Maas et al. [3]. The effectiveness of the catalysts followed the
order [Cu(OTf)] > [Ru2(CO)4(m-Ac)2]n ꢀ [Rh2(pfb)4] >> [Rh2(OAc)4] (pfb ˆ per-
fluorobutanoate). The inefficiency of [Rh2(OAc)4] in the decomposition of diazo-
(trialkylsilyl)acetates has been reported by other authors [4]. In spite of this, RhII
carboxylate catalysts have been used successfully for diazo decomposition of a-
silylated diazo esters. Marsden and co-workers reported intramolecular CH insertions
of silylated diazo esters in the presence of rhodium(II) octanoate in refluxing benzene
[5]. Under similar conditions, silylated diazo ketones rearrange to silyl ketenes when
exposed to [Rh2(O2CC7H15)4] [6]. Bolm et al. described the [Rh2(OAc)4]-catalyzed
decomposition of diazo(trialkylsilyl)acetates in toluene at 40 708 for the preparation
of trialkylsilyl-substituted a-amino acids via carbene insertion into NH bonds [7].
We have recently investigated RhII-catalyzed enantioselective intramolecular CH
insertions of alkyl diazo(trialkylsilyl)acetates [8]. Reactions carried out with
[Rh2(OAc)4] required elevated temperatures (refluxing benzene) to effect diazo
decomposition. However, we were surprised to find that the RhII catalysts of
Hashimoto and Ikegami [9][10] were so much more efficient than [Rh2(OAc)4] that
the reactions could be carried out at 208 in toluene. The Hashimoto catalysts use
¹ 2004 Verlag Helvetica Chimica Acta AG, Z¸rich

Helvetica Chimica Acta Vol. 87 (2004)
2849
phthaloyl-protected amino acids such as phenylalanine and tert-leucine (ˆ2-amino-3,3-
dimethylbutanoic acid) as ligands for dimeric RhII. They are sterically more hindered
than [Rh2(OAc)4], yet they are more reactive. The reasons for this enhanced reactivity
were not investigated and are subject to speculation. However, a plausible explanation
based on the acidity of the ligands may be advanced: the reactivity of the RhII catalysts
depends strongly upon the pKa value of the ligand. Thus, RhII carboxylates are much
more efficient in diazo decompositions than RhII carboxamidates [11]. The pKa value
for N-phthaloylglycine is 3.26, ca. 1.5 units below that of acetic acid. Other
phthaloylated amino acids have a pKa value in the range of 3.46 3.84 [12].
Conceivably, the presence of four ligands of higher acidity than acetic acid may be at
least in part responsible for the enhanced reactivity of RhII catalysts having phthaloyl-
protected amino acids as ligands in comparison to that of [Rh2(OAc)4] or other RhII
carboxylates. This enhanced catalyst reactivity is crucial for the successful decom-
position of silylated diazo esters under mild conditions.
In the intramolecular CH insertion of alkyl diazo(triethylsilyl)acetates, we have
found enantioselectivities of up to 79% at 208. In this communication, we report results
on RhII-catalyzed inter- and intramolecular cyclopropanations of olefins.
2. Results and Discussion.
2.1. Intermolecular Cyclopropanation. The cyclo-
propanations were carried out with ethyl diazo(triethylsilyl)- and diazo(dimethylphen-
ylsilyl)acetate (1a and 1b, resp.). The acetate 1a was synthesized in high yield from
ethyl diazoacetate and triethylsilyl trifluoromethanesulfonate (TfOSiEt3) [13], and 1b
from chlorodimethylphenylsilane (Scheme 1) [3][14]. The decomposition of 1a with
[Rh2(OAc)4] in refluxing toluene in the presence of 10 equiv. of styrene afforded the
cyclopropane derivative 2a in 23% yield and a trans/cis ratio of 74 :26 (Table 1). This
ratio agrees well with that of 3.4 :1reported by Maas et al. [3] for methyl
diazo(trimethylsilyl)acetate. The relative configurations of the cyclopropane deriva-
1
tives 2a were assigned upon comparison of their H-NMR spectra with those of the
corresponding methyl esters of known configurations. The resonance for HÀC(2) in
trans-2a (d 2.46) is shifted upfield by ca. 0.3 ppm relative to that of cis-2a (d 2.76). In
Scheme 1

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Helvetica Chimica Acta Vol. 87 (2004)
Table 1. Cyclopropanation of Styrene with Ethyl Diazo(triorganylsilyl)acetates 1a,b
Catalysta)
Time
Temp. Solvent Styrene Product Yield [%] trans/cis ee [%]
[equiv.]
trans cis
1a [Rh2(OAc)4]
1h
1.5 h
1.66 h r.t.
1h
reflux PhMe
r.t. PhMe
CH2Cl2 10
10
2a
2a
2a
2a
2a
2a
2a
2a
2b
2b
2b
23
40
40
69
72
70
43
32
39
70
68
74 : 26
82 : 18
82 : 18
82 : 18
81: 19
77 : 23
75 : 25
68 : 32
86 : 14
88 : 12
85 : 15
1a [Rh2{(S)-nttl}4]
1a [Rh2{(S)-nttl}4]
1a [Rh2{(S)-nttl}4]
1a [Rh2{(S)-pttl}4]
1a [Rh2{(S)-bpttl}4] 12 h
1a [Rh2{(R)-bptv}4] 12 h
1a [Rh2{(S)-ptpa}4] 12 h
1b [Rh2(OAc)4]
1b [Rh2{(S)-pttl}4]
1b [Rh2{(R)-bptv}4] 12 h
5
n.d.
n.d.
n.d.
n.d.
r.t.
r.t.
r.t.
r.t.
r.t.
PhMe
PhMe
PhMe
PhMe
PhMe
10
10
54b) 27b)
b
4 h
48
)
30b)
10
10
10
10
10
10
23b) n.d.
30c) n.d.
34b) 41b)
1.5 h
0.5 h
reflux PhMe
r.t.
r.t.
PhMe
PhMe
n.d.
n.d.
n.d.
n.d.
a) See Fig. 1 for the ligand structures. b) Absolute configuration of major component: trans-2a, (1S,2R); cis-2a,
(1R,2R). c) Absolute configuration of major component: trans-2a, (1R,2S), cis-2a, (1S,2S).
addition, the methylene group of the ester function of trans-2a, which is situated cis to
the Ph group, appears at higher field (d 3.80) than in cis-2a (d 4.22), where it is trans.
The preference for formation of trans-2a where the Ph and COOEt groups are cis is of
some interest since in the cyclopropanation with ethyl diazoacetate, the trans-isomer
usually predominates. However, upon protiodesilylation with Bu4NF, epimerization
occurred, and the desilylated cyclopropane 3 was isolated as a 70 :30 trans/cis mixture,
even when the reaction was carried out at À 788.
The cyclopropanation of styrene with 1a was then carried out in the presence of
chiral RhII carboxylate catalysts of the Hashimoto type, and the results are reported in
Table 1 (for structures and abbreviations of catalysts, see Fig. 1).With [Rh2{(S)-nttl}4]
or [Rh2{(S)-pttl}4] as the catalyst in toluene, the reaction proceeded smoothly at room
temperature. With a 10-fold excess of styrene, yields of 69 and 72% of cyclopropane
derivatives 2a were obtained, respectively. The yield of 2a decreased significantly when
the excess of styrene was reduced to five-fold or when the reaction was carried out in
CH2Cl2. GC Separation of the enantiomers of the cyclopropane derivatives 2a failed,
but could be achieved upon their reduction with LiAlH4 to a diastereomer trans/cis
mixture 4. The relative configuration of the diastereoisomers 4 was verified by
comparison of the NMR signals of the CH2OH group with those reported in the
literature for the trimethylsilyl analogues of 4 [3]. Separation of the enantiomers was
not perfect; however, the modest enantioselectivities achieved in these reactions (up to
54% for trans-2a and up to 41% for cis-2a) do not warrant the development of a more
appropriate analytical method at this time. The alcohols 4 failed to undergo
protiodesilylation upon exposure to Bu4NF even upon prolonged reaction times.
For the determination of the absolute configuration of 2a, a 83 :17 mixture of
(1R,2R)-ethyl 2-phenylcyclopropane-1-carboxylate (trans-3) and of its isomer cis-3
having (1R,2S)-configuration was synthesized by Cu-catalyzed cyclopropanation of
styrene with ethyl diazoacetate in the presence of the chiral bis[dihydrooxazole] ligand
6 [15] (Scheme 2). Comparison of the retention times (b-Dex column) with that of the
isomer mixture 3 obtained after desilylation of the cyclopropane derivatives 2a

Helvetica Chimica Acta Vol. 87 (2004)
2851
Fig. 1. Ligands and abbreviations of the corresponding RhII catalysts
Scheme 2
(isolated from the reaction with [Rh2{(S)-pttl}4] and [Rh2{(S)-nttl}4]), allowed
assignment of the (1S,2S)-configuration of the major enantiomer of trans-3 and the
(1R,2S)-configuration to the major isomer of cis-3. Application of the CIP rules affords
cis-2a with predominant (1R,2R) and trans-2a with predominant (1S,2R) configuration.
Note that, because epimerization occurred at C(1) upon protiodesilylation of the
trans/cis-mixture 2a, trans- and cis-3 have the same ee. The expected ee of trans-3
resulting from reaction with [Rh2{(S)-pttl}4], assuming total equilibration of the
epimers, is 43%, close to the observed value of 45% (Fig. 2). For catalysis with
[Rh2{(S)-nttl}4], the calculated and experimental values are 49 and 51%, respectively
(Fig. 2).
Some cyclopropanations were carried out with ethyl diazo(dimethylphenylsilyl)-
acetate (1b) to afford cyclopropane derivatives 2b as a ca. 88 :1 5trans/cis stereoisomer
mixture. As before, the enantiomers of 2b were not separable. Protiodesilylation of
trans/cis 2b 88 :12 gave a mixture of (1S,2S)-trans-3 (31%, 15% ee) and (1R,2S)-cis-3
(18%, 13% ee). Accordingly, the absolute configuration of trans-2b is (1S,2R), and that
of cis-2b is (1R,2R). Determination of the ee of the isomers 2b via reduction to the

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Helvetica Chimica Acta Vol. 87 (2004)
Fig. 2. Enantiomer excesses (ee) of 2a, 3, and 4
corresponding alcohols failed. The 88 :15 trans/cis-mixture 2b resulting from reaction
with [Rh2{(R)-bptv}4] was converted to the known [16] alcohol trans-5 in a mediocre
yield of 24% with mercuric acetate/peracetic acid (Scheme 1). The cis-isomer was not
detectable in the reaction mixture. Furthermore, the enantiomers of 5 could not be
separated.
2.2. Intramolecular Cyclopropanation. The intramolecular cyclopropanation of
allylic diazoacetates in the presence of chiral RhII carboxamidate catalysts, such as
[Rh2{(S)-mepy}4], was the first successful application of RhII carboxamidate catalysts
and provided enantioselectivities close to 100% [17]. We have now investigated the
analogous reaction with several (triethylsilyl)-substituted allyl diazoacetates with the
objective of opening enantioselective access to functionalized cis-disubstituted cyclo-
propane derivatives. The diazo esters 7a d required as precursors are known
(Scheme 3). They were synthesized from the corresponding alcohols and the acetone
adduct of ketene, as described previously [18]. Details and full characterization are
found elsewhere [19]. Silylation of the diazo esters to afford 8a d was effected with
TfOSiEt3 in the presence of diisopropylethylamine (iPr2NEt) [20].
The diazo decomposition of the silylated ester 8a was investigated with a large
selection of catalysts (Table 2). [Rh2(OAc)4] and the RhII carboxamidate catalysts were
inefficient even at elevated temperatures and provided only poor yields of cyclo-
propane derivative 9a. Satisfactory results were obtained, however, with RhII
carboxylates derived from protected amino acids in toluene at room temperature.
The structure of 9a was established by comparison of its spectral data with those of the
corresponding trimethylsilyl analogue, which are available in the literature [21]. The
highest yield of 85% resulted from the reaction catalyzed by [Rh2{(S)-tbsp}4], thus
demonstrating that sulfonylated proline is as efficient as the Hashimoto-type ligands.
The highest enantioselectivity in toluene (54%) was obtained with [Rh2{(S)-bpttl}4],

Helvetica Chimica Acta Vol. 87 (2004)
2853
Scheme 3
Table 2. Intramolecular Cyclopropanation of Allyl Diazo(triethylsilyl)acetate (8a)a)
Catalystb)
Time
Temp.
Solvent
Yield [%] of 9a
ee [%]
Conf.
[Rh2(OAc)4]
1.5 h
12 h
15 h
4 h
2.5 h
3 h
reflux
reflux
reflux
reflux
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhCF3
PhMe
PhCF3
PhMe
PhMe
PhMe
CH2Cl2
pentane
PhCF3
32
0
5
[Rh2{(S)-mepy}4]
[Rh2{(S)-meox}4]
[Rh2{(S)-bnaz}4]
[Rh2{(S)-pttl}4]
[Rh2{(S)-nttl}4]
[Rh2{(S)-ptpa}4]
[Rh2{(S)-tbsp}4]
[Rh2{(S)-dosp}4]
[Rh2{(R)-bptv}4]
[Rh2{(R)-bptv}4]
[Rh2{(S)-bptpa}4]
[Rh2{(S)-bptpa}4]
[Rh2{(S)-bpttl}4]
[Rh2{(S)-bpttl}4]
[Rh2{(S)-bpttl}4]
[Rh2{(S)-bpttl}4]
[Rh2{(S)-bpttl}4]
[Rh2{(S)-bpttl}4]
0
4
17
79
74
62
85
64
76
78
76
82
76
0
(1R,5S)
(1S,5R)
(1S,5R)
(1S,5R)
(1R,5S)
(1R,5S)
(1R,5S)
(1R,5S)
(1S,5R)
(1S,5R)
(1S,5R)
24
18
11
18
18
11
14
53
56
54
2 h
3.5 h
2.5 h
2.25 h
2 h
1.5 h
12 h
2.5 h
6 h
2 h
3 h
3 h
3 h
r.t.
À 788
08
r.t.
r.t.
r.t.
78
82
62
75
17
15
16
53
(1S,5R)
(1S,5R)
(1S,5R)
(1S,5R)
a) With 2% of catalyst. b) See Fig. 1 for the ligand structures.
although [Rh2{(S)-bptpa}4] was comparable with 53%. Surprisingly, with [Rh2{(S)-
bpttl}4], the ee at 08 was lower (17%) than at room temperature, and no reaction
occurred at À 788. Among the various solvents tried, toluene and a,a,a-trifluoroto-
luene (ˆ(trifluoromethyl)benzene) afforded the best results, while CH2Cl2 and
pentane were unsatisfactory. The absolute configuration of 9a was assigned by its

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Helvetica Chimica Acta Vol. 87 (2004)
conversion to 10a by protiodesilylation with Bu4NF and comparison of its GC retention
time with that of authentic (1R,5S)-10a, which was prepared directly with 97% ee from
7a in the presence of [Rh2(S)-mepy}4] [17]. The majority of catalysts afforded silylated
cyclopropanes 9a of configuration (1S,5R), which led to (1R,5S)-10a upon protiode-
silylation.
The results are disappointing in comparison to those obtained with unsilylated
allylic diazo esters 7, where enantioselectivities of > 98% have been observed with
[Rh2{S)-mepy}4]. Unfortunately, as mentioned above, the RhII carboxamidate catalysts,
which perform best with unsilylated allyl diazoacetates 7, are not sufficiently reactive to
decompose the silylated analogues. Similarily, no diazo decomposition occurred with
the ortho-metallated [RhII(phosphine)] complexes of Lahuerta et al. [22].
The intramolecular cyclopropanations of the silylated diazo esters 8b,c were less
satisfactory. The cinnamyl derivative 8b reacted with [Rh2{(S)-nttl}4] and [Rh2{(S)-
bpttl}4] to afford the cyclopropane 9b in only 9 and 10% yield, respectively (Table 3).
The −exo×-orientation of the Ph substituent in 9b was assigned on the grounds of the
coupling constant of 4.5 Hz for HÀC(6), typical for vicinal trans-coupling of
cyclopropane protons [23]. This is consistent with the generally observed stereospecific
cyclopropanation of allylic diazo esters in the presence of RhII or Cu catalysts. An
analogous trans-coupling of 3.7 Hz has been reported for the desilylated 10b [24].
Table 3. Intramolecular Cyclopropanation of Silylated Diazoacetates 8b d in PhMe
Catalysta)
Time
Temp.
Product
Yield [%]
ee [%]
Conf.
Other product
8b
8b
8c
8c
8d
8d
8d
8d
[Rh2{(S)-nttl}4]
[Rh2{(S)-bpttl}4]
[Rh2(OAc)4]
[Rh2{(S)-nttl}4]
[Rh2(OAc)4]
[Rh2{(S)-pttl}4]
[Rh2{(S)-nttl}4]
[Rh2{(S)-bpttl}4]
2.5 h
2.5 h
1h
3.5 h
1.5 h
2 h
r.t.
r.t.
reflux
r.t.
reflux
r.t.
r.t.
9b
9b
9c
9c
9d
9d
9d
9d
9
10
9
20
36
77
76
69
n.d.
n.d.
n.d.
n.d.
30
n.d.
11 (18%)
31(1
38
28
S,5R,6R)
(1S,5R,6R)
(1S,5R,6R)
1h
12 h
r.t.
a) See Fig. 1 for the ligand structures.
The diazo decomposition of 8b was accompanied by formation of secondary
products, the structure of which could not be established. However, a b-lactone may be
implicated (see below). Owing to the poor yield of 9b and to difficulties in the
enantiomer separation, the reaction of 8b was not pursued. The diazo decomposition of
the 2-methyl substituted diazo acetate 8c, in turn, proceeded to 9c in mediocre yield of
ca. 20% with up to 30% ee, and was accompanied by formation of b-lactone 11 (15
18% yield). In contrast, the reaction proceeded well with the (2Z)-pent-2-enyl diazo
ester 8d, which resulted in yields of ca. 70% of cyclopropane derivative 9d. The
structure of 9d was confirmed via its protiodesilylation with Bu4NF in THF to afford
known 10d, which was used for the determination of the ee. The absolute configuration
of 9d was determined to be (1S,5R,6R) by comparison of the GC retention times of the

Helvetica Chimica Acta Vol. 87 (2004)
2855
desilylated 10d (1R,5S,6R) with those of an authentic sample of (1R,5S,6R)-10d
prepared from 7d in the presence of [Rh2{(S)-mepy}4] [1 7].
3. Conclusions. The present results show that the diazo decomposition of a-
silylated diazo acetates may be carried out under mild conditions and affords
acceptable yields of cyclopropane derivatives. The RhII-catalysts presently available do
not allow to reach enantioselectivities comparable to those resulting from the
unsilylated analogues. In addition, the protiodesilylation of silylated cyclopropanecar-
boxylates proceeds with epimerization, unless epimerization is precluded for skeletal
reasons, and the oxydative replacement of silyl groups adjacent to carbonyl functions
proceeds with poor yields. These problems have yet to be overcome to make silylated
diazo esters attractive reagents for enantioselective carbene transfer.
This work was supported by the Swiss National Science Foundation (Projects No. 20-52581.97 and 2027-
048156). Support and sponsorship concerted by COST Action D24 Sustainable Chemical Processes:
Stereoselective Transition-Metal-Catalysed Reactions are kindly acknowledged. The authors are indebted to
L. Nicolas for carrying out parts of the experiments, A. Pinto and J.-P. Saulnier for the NMR spectra, and D.
Klink for the mass spectra.
Experimental Part
1. General. See [25]. The catalysts (see Fig. 1) were synthesized according to published procedures:
[Rh2{(S)-mepy}4] [26], [Rh2{(S)-meox}4] [27], [Rh2{(S)-bnaz}4] [11c], [Rh2{(S)-ptpa}4] [9], [Rh2{(S)-pttl}4] [9],
[Rh2{(S)-pttl}4] [10], [Rh2{(S)-bptpa}4] [10], [Rh2{(R)-bptv}4] [10], [Rh2{(S)-tbsp}4] [28], [Rh2{(S)-dosp}4] [29],
and [Rh2{(S)-nttl}4] [30].
2. Intermolecular Cyclopropanation of Styrene. 2.1. Ethyl Diazo(triethylsilyl)acetate (1a) [31 ] was
synthesized from ethyl diazoacetate and TfOSiEt3 according to [18]. IR (film): 2957s, 2094w, 1677m, 1271w.
1H-NMR (500 MHz, CDCl3): 0.75 (q, J ˆ 8.1, 6 H); 0.98 (t, J ˆ 8.3, 9 H); 1.26 (t, J ˆ 7.2, 1H); 4.18 ( q, J ˆ 7.2,
‡
2 H). 13C-NMR (75 MHz, CDCl3): 3.2 (t); 7.0 (q); 14.4 (q); 60.6 (t); 69.6 (s). MS: 228 (5, M ), 200 (7), 199 (48),
183 (10), 171 (15), 143 (12), 131 (100), 115 (30), 103 (61), 99 (17), 87(67), 75(39), 59(43). HR-MS: 228.1310
‡
(C10H20O2N2Si ; calc. 228.1294).
2.2. Ethyl Diazo(dimethylphenylsilyl)acetate (1b) [3][12]. To ethyl diazoacetate (6.0 mmol) in Et2O (1 5 ml)
was added, at 08, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, 1.34 ml, 8.9 mmol) and chlorodimethylphenylsilane
(380 ml, 8.9 mmol). After 20 h of stirring at r.t., Et2O (25 ml) was added, and the mixture was washed with H2O
(25 ml). The org. layer was dried (MgSO4) and evaporated: 1b (1.44 g, 98%). Yellow oil after FC (SiO2,
pentane/AcOEt 80 :20). IR (film): 2983w, 2088s, 1682s, 1257s, 1073m, 820m. 1H-NMR (300 MHz, CDCl3): 0.57
(s, 6 H); 1.23 (t, J ˆ 7.14, 3 H); 4.18 (q, J ˆ 7.0, 2 H); 7.20 7.30 (m, 5 H); 7.42 7.45 (m, 3 H); 7.61 7.65 ( m, 2 H).
13C-NMR (75 MHz, CDCl3): À 3.0 (q); 14.2 (t); 60.6 (t); 127.9 (d); 129.8 (d); 133.7 (d); 135.3 (d); 169.0 (s). MS:
‡
‡
248 (7, M ), 205 (33), 177 (51), 135 (80), 103 (76), 75 (100), 59 (23). HR-MS: 248.0980 (C12H16O2N2Si ; calc.
248.0981).
2.3. Cyclopropanation of Styrene. General Procedure. To the RhII catalyst (2 mol-%) under Ar, styrene
(920 ml, 8.0 mmol) and the silylated diazo acetate 1a,b (0.85 mmol were added). The mixture was heated to the
temp. indicated in Table 1 until decomposition of the diazo ester was completed (ca. 2 h). The solvent was
evaporated, and the crude cyclopropane derivative was purified by FC. The diastereoisomers were not
separated, but their NMR data could be extracted from mixtures.
Ethyl cis- and trans-2-Phenyl-1-(triethylsilyl)cyclopropane-1-carboxylate (2a). Separation of diastereoiso-
mers by GC (anal. b-Dex, 5 min 1408, then 18/min for 10 min to 1808): tR 36.2 (trans-2a) and 36.6 (cis-2a). 2a: IR
‡
(film): 2958w, 2878w, 1714s, 1461m, 1208m, 1004m, 698s. MS: 304 (7, M ), 275 (15), 231 (19), 135 (19), 131
‡
(100), 115 (40), 87 (70), 75 (35), 59 (37). HR-MS: 304.1849 (C18H28O2Si ; calc. 304.1858).
1
trans-2a: H-NMR (300 MHz, CDCl3): 0.68 0.76 (m, 6 H); 1.08 (t, J ˆ 7.7, 9 H); 1.20 1.26 (m, 1H); 1.36
(t, J ˆ 7.0, 3 H); 1.96 (dd, J ˆ 6.4, 4.9, 1H); 2.46 ( t, J ˆ 7.2, 1H); 3.80 ( qd, J ˆ 7.2, 0.8, 2 H); 7.20 7.32 (m, 5 H).
13C-NMR (75 MHz, CDCl3): 2.8 (t); 7.6 (q); 13.5 (t); 13.9 (q); 27.5 (d); 60.1( t); 126.4 (d); 126.9 (d); 128.5 (d);
137.5 (s); 172.3 (s).

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Helvetica Chimica Acta Vol. 87 (2004)
1
cis-2a: H-NMR (300 MHz, CDCl3): 0.25 0.48 (m, 6 H); 0.85 (t, J ˆ 7.9, 9 H); 0.92 (t, J ˆ 7.1 , 3 H); 1 .44
1.48 (m, 1H); 1.80 ( dd, J ˆ 8.8, 4.0, 2 H); 2.76 (dd, J ˆ 7.0, 8.8, 1H); 4.22 ( qd, J ˆ 7.1, 0.8, 2 H); 7.20 7.32
(m, 5 H). 13C-NMR (100 MHz, CDCl3): 3.8 (t); 7.7 (q); 14.3 (q); 16.0 (t); 31.6 (d); 60.7 (t); 127.9 (d); 128.0 (d);
130.0 (d); 138.3(s); 172.3 (s).
Ethyl cis-and trans-1-(Dimethylphenylsilyl)-2-phenylcyclopropane-1-carboxylate (2b). Separation of dia-
stereoisomers by GC (anal. permabond, 5 min 1208, then 18/min for 30 min to 1808): tR 63.5 (cis) and 64.4 (trans).
‡
2b: IR (film): 2971w, 1716s, 1427m, 1275s, 1108s. MS: 324 (9, M ), 246 (9), 144 (12), 136 (14), 135 (100), 107
‡
(14), 103 (21), 75 (11). HR-MS: 324.1545 (C20H24O2Si ; calc. 324.1546).
trans-2b: 1H-NMR (300 MHz, CDCl3): 0.52 (s, 3 H); 0.55 (s, 3 H); 0.89 (t, J ˆ 7.17, 3 H); 1.15 1.20
(m, 1H); 2.02 ( m, 1H); 2.45 ( t, J ˆ 8.3, 1H); 3.77 ( dd, J ˆ 1.1, 7.17, 2 H); 7.20 7.30 (m, 5 H); 7.42 7.44
(m, 5 H); 7.64 7.67 (m, 2 H). 13C-NMR (75 MHz, CDCl3): À 3.6 (q); À 2.1( q); 13.9 (t); 14.4 (t); 22.6 (s); 28.2
(d); 60.2 (t); 126.4 (d); 127.7 (d); 127.8 (d); 128.7 (d); 129.3 (d); 134.2 (d); 136.7 (s); 137.0 (s); 172.0 (s).
cis-2b: 1H-NMR (300 MHz, CDCl3): 0.52 (s, 3 H); 0.55 (s, 3 H); 0.89 (t, J ˆ 7.2, 3 H); 1.61 (dd, J ˆ 4.0, 6.8,
1H); 1.88 ( dd, J ˆ 4.0, 8.9, 1H); 2.89 ( dd, J ˆ 6.8, 8.7, 1H); 4.14 ( q, J ˆ 7.2, 2 H); 7.20 7.30 (m, 5 H); 7.42 7.44
(m, 5 H); 7.64 7.67 (m, 2 H). 13C-NMR (75 MHz, CDCl3): À 2.6 (q); À 2.1( q); 13.9 (t); 16.1 (t); 19.8 (s); 32.5
(d); 60.2 (t); 126.8 (d); 127.3 (d); 127.9 (d); 128.5 (d); 130.0 (d); 133.9 (d); 136.7 (s); 137.0 (s); 172.0 (s).
2.4. Desilylation of 2a and 2b: Ethyl trans- and cis-2-Phenylcyclopropane-1-carboxylate (3). To a 81:19
mixture of trans(48% ee)- and cis(30% ee)-2a (142 mg, 0.56 mmol) in THF (3.0 ml) was added 1m Bu4NF
(1.0 ml) in THF at À 788. The temp. was allowed to reach r.t. After stirring for 2 4 h, the mixture was quenched
with H2O (2.0 ml) and extracted with CH2Cl2. The org. layer was dried (MgSO4) and evaporated and the residue
purified by FC (SiO2, pentane/AcOEt 97:3); 70 :30 mixture of (1S,2S)-trans-3 (45% ee) and (1R,2S)-cis-3 (45%
ee) in 81% yield.
Similarly, starting from a mixture of trans(54% ee)- and cis(27% ee)-2a 4 :1 ,trans- and cis-3 were obtained
in a 82 :18 ratio and with 51% ee (trans-3) and 49% ee (cis-3), resp.
The same procedure was applied to the trans/cis-2b 88 :12 (100.5 mg, 0.31 mmol) from reaction with
[Rh2{(S)-pptl}4]), which afforded (1S,2S)-trans-3 (31%, 15% ee) and (1R,2S)-cis-3 (18%, 13% ee).
trans-3: Enantiomer separation by GC (see below). IR (film): 2982w, 1725s, 1185s, 755m, 698m. 1H-NMR
(300 MHz, CDCl3): 1.26 (t, J ˆ 7.2, 3 H); 1.56 1.68 (m, 1 H); 1.86 1.92 (m, 1H); 2.48 2.54 ( m, 1H); 4.16
(q, J ˆ 7.2, 2 H); 7.07 7.30 (m, 5 H). 13C-NMR (75 MHz, CDCl3): 14.3 (q); 17.0 (t); 24.1( d); 26.1( d); 60.6 (t);
‡
126.1 (d); 126.4 (d); 128.4 (d); 140.1 (s); 173.4 (s). MS: 190 (33, M ), 145 (23), 117 (100), 115 (50), 91 (21). HR-
‡
MS: 190.0981 (C12H14O2 ; calc. 190.0994).
cis-3: Enantiomer separation by GC (see below). IR (film): 3009w, 1721s, 1186s, 1081w, 864w. 1H-NMR
(300 MHz, CDCl3): 0.93 (t, J ˆ 7.2, 3 H); 1.27 1.35 (m, 2 H); 1.70 1.76 (m, 1H); 2.05 2.13 ( m, 1H); 2.59
(m, 1H); 3.88 ( q, J ˆ 7.2, 2 H); 7.20 7.28 (m, 5 H). 13C-NMR (75 MHz, CDCl3): 11.0 (t); 13.9 (q); 21.8 (d); 25.4
‡
(d); 60.1( t); 126.6 (d); 127.8 (d); 129.3 (d); 136.6 (s); 170.9 (s). MS: 190 (32, M ), 145 (20), 117 (100), 115 (53),
‡
91 (23). HR-MS: 190.1003 (C12H14O2 ; calc. 190.0994).
2.5. Cyclopropanation of Styrene with Ethyl Diazoacetate. To the bis[dihydrooxazole] ligand 6 (1.3 mol-%),
[Cu(OTf)2] (1.3 mol-%), and styrene (1.25 ml, 5.0 equiv.) in CHCl3 (6.0 ml), ethyl diazoacetate (257 mg,
1.0 equiv.) in CHCl3 (6.0 ml) was added dropwise. The mixture was stirred at r.t. for 1h and then evaporated.
The crude product was purified by FC: 129 mg (30%) of an 83 :17 mixture of (1R,2R)-trans-3 (83% ee) and
(1R,2S)-cis-3 (70% ee).
Ethyl trans-(1R,2R)-2-Phenylcyclopropane-1-carboxylate (trans-3). Enantiomer separation by GC (b-Dex,
5 min at 808, then 18/min, 10 min at 1808): tR 55.3 ((1R,2R), major) and 55.5 ((1S,2S), minor).
Ethyl cis-(1R,2S)-2-Phenylcyclopropane-1-carboxylate (cis-3). Enantiomer separation by GC (b-Dex,
5 min at 808, then 18/min, 10 min at 1808): tR 51.7 ((1S,2R), minor) and 52.2 ((1R,2S), major).
2.6. Reduction of 2a: trans- and cis-2-Phenyl-1-(triethylsilyl)cyclopropane-1-methanol (4). To LiAlH4
(2 equiv.) in THF (2.0 ml) under Ar, trans/cis-2a 3 :1(0.80 mmol) in THF (4.0 ml) was added. The mixture
was stirred overnight at r.t. Excess LiAlH4 was decomposed by addition of ethane-1,2-diamine (2 ml), followed
by 8% NaOH soln. (2.0 ml) and H2O. The crude product was extracted with Et2O (10 ml), the extract dried
(Na2SO4) and evaporated, and the resulting diasteroisomer mixture separated by FC (SiO2, CH2Cl2/pentane
80 :20).
trans-4: Yield 45%. Colorless oil. Enantiomer separation by GC (b-Dex, 5 min at 1408, then 0.58/min to
1808, 10 min at 1808): tR 48.6 ((1S,2S), minor) and 49.1((1 R,2R), major); absolute configuration assigned from
that of trans-2a. IR (film): 2945m, 2871m, 1458w, 1239w, 1003s, 726s. 1H-NMR (300 MHz, CDCl3): 0.68 (q, J ˆ
7.9, 6 H); 0.87 0.99 (m, 2 H); 1.05 (t, J ˆ 7.9, 9 H); 2.24 (t, J ˆ 6.7, 1H); 3.22 ( d, J ˆ 11.8, 1 H); 3.53 (d, J ˆ 11.8,
1H); 7.24 7.30 ( m, 5 H). 13C-NMR (75 MHz, CDCl3): 2.6 (t); 7.6 (q); 11.7 (t); 15.9 (s); 24.3 (d); 65.7 (t); 126.2

Helvetica Chimica Acta Vol. 87 (2004)
2857
‡
(d); 128.3 (d); 128.9 (d); 138.4 (s). MS: 233 (12, [M À C2H5] ), 215 (27), 130 (36), 115 (43), 103 (100), 87 (65),
‡
75 (80). HR-MS: 233.1386 (C14H21OSi ; calc 233.1362).
cis-4: Yield 13%. Colorless oil. Enantiomer separation by GC (b-Dex, 5 min 1208, then 18/min to 1808,
10 min 1808): tR 57.0 ((1R,2R), major) and 57.3 ((1S,2S), minor); absolute configuration assigned based on that
of cis-2a. IR (film): 2951m, 2874m, 1455w, 1238w, 1005s, 726s. 1H-NMR (300 MHz, CDCl3): 0.24 0.40 (m, 6 H);
0.85 (t, J ˆ 7.7, 9 H); 1.20 (t, J ˆ 5.6, 1H); 1.47 ( s, 1H); 2.10 2.20 ( m, 2 H); 3.27 (d, J ˆ 11.0, 1 H); 3.87 (d, J ˆ
11.0, 1 H); 7.20 7.30 (m, 5 H). 13C-NMR (75 MHz, CDCl3): 3.3 (t); 7.6 (q); 12.0 (t); 17,6 (s); 27.0 (d); 71.5 (t);
‡
126.2 (d); 127.9 (d); 129.7 (d); 139.7 (s). MS: 233 (8, [M À C2H5] ), 215 (21), 171 (12), 130 (39), 115 (39), 103
‡
(100), 87 (60), 75 (85). HR-MS: 233.1372 (C14H21OSi ; calc. 233.1361).
2.7. Oxydative Desilylation of trans/cis-2b: Ethyl trans-1-Hydroxy-2-phenylcyclopropane-1-carboxylate
(trans-5). Peracetic acid (6.0 ml; 35% in AcOH) was added to trans/cis-2b 78 :23 (204 mg, 0.61mmol) and
Hg(OAc)2 (233 mg, 0.73 mmol). After stirring overnight at r.t., the mixture was diluted with Et2O (100 ml).
After slow addition of sat. thiosulfate, the org. layer was washed with H2O (2 Â 100 ml) and 5% NaHCO3 soln.
(50 ml) and evaporated. Purification by FC (SiO2, pentane/AcOEt 80 :20) afforded trans-5 (31mg, 24%). IR
(film): 3451w, 2978w, 1722m, 1180m, 1015m. 1H-NMR (300 MHz, CDCl3): 0.76 (t, J ˆ 7.1, 3 H); 1.66 (dd, J ˆ
10.3, 6.0, 1 H); 1.97 (dd, J ˆ 8.6, 6.0, 1H); 2.77 ( t, J ˆ 9.6, 1H); 3.77 3.87 ( m, 2 H); 7.17 7.27 (m, 5 H).
13C-NMR (75 MHz, CDCl3): 13.5 (q); 18.6 (t); 34.5 (d); 60.8 (s); 61.1 (t); 126.6 (d); 127.9 (d); 128.9 (d); 135.9 (s);
172.5 (s).
3. Intramolecular Cyclopropanation of Allyl Diazo(triethylsilyl)acetates 7. 3.1. Allyl Diazoacetates 7a d.
The diazo precursors 7a d were synthesized according to literature procedures from the appropriate allylic
alcohols and 2,2,4-trimethyl-1,3-dioxacyclohex-4-en-6-one (ˆ2,2,6-trimethyl-4H-1,3-dioxin-4-one) in refluxing
xylene. The resulting acetoacetate esters underwent diazo transfer to afford diazoacetoacetates, which were
subjected to cleavage with base to yield the diazo esters 7a d [18][19].
3.2. Silylation of Allyl Diazoacetates 7a d: Allyl Diazo(triethysilyl)acetates 8a d, General Procedure.
iPr2NEt (290 ml, 1.66 mmol) followed by TfOSiEt3 (380 ml, 1.66 mmol) in Et2O (2.5 ml) was added, at À 788, to
the diazo acetate 7a d (1.50 mmol) in Et2O (5.0 ml). After stirring overnight at r.t., the mixture was neutralized
with Na2CO3, filtered, and evaporated. The residue was purified by FC.
Prop-2-enyl Diazo(triethylsilyl)acetate (8a) [19]. From allyl diazoacetate [32] after FC (SiO2, pentane/
AcOEt 97:3): yield 81%. IR (film): 2955m, 2090s, 1687s, 1254s. 1H-NMR (500 MHz, CDCl3): 0.75 0.83
(m, 6 H); 1.01 (t, J ˆ 7.4, 9 H); 4.66 (td, J ˆ 1.5, 5.6, 2 H); 5.24 5.37 (m, 2 H); 5.89 6.02 (m, 1 H). 13C-NMR
‡
(125 MHz, CDCl3): 3.1( t); 7.1( q); 65.3 (t); 117.9 (t); 132.5 (d); 169.1 (s). MS: 240 (<1, M ), 217 (1), 183 (20),
‡
143 (21), 115 (80), 87 (100), 59 (70). HR-MS: 240.1306 (C11H20O2N2Si ; calc. 240.1294).
(2E)-3-Phenylprop-2-enyl Diazo(triethylsilyl)acetate (8b). From trans-cinnamyl diazoacetate [17][19][33]
after FC (SiO2, pentane/AcOEt 90 :10): yield 72%. Yellow oil. IR (film): 2955w, 2876w, 2084s, 1683s, 1255s,
736m. 1H-NMR (500 MHz, CDCl3): 0.81( q, J ˆ 7.9, 6 H); 1.04 (t, J ˆ 7.9, 9 H); 4.83 (d, J ˆ 6.4, 2 H); 6.29 (td, J ˆ
6.2, 15.8, 1 H); 6.66 (d, J ˆ 15.8, 1 H); 7.27 7.42 (m, 5 H). 13C-NMR (125 MHz, CDCl3): 3.1( t); 7.0 (q); 65.1( t);
‡
123.5 (d); 126.6 (d); 128.0 (d); 128.6 (d); 133.8 (d); 136.3 (s); 169.2 (s). MS: 316 (2, M ), 259 (11), 217 (6), 117
‡
(100), 115 (32), 87 (22), 59 (13). HR-MS: 316.1609 (C17H24O2N2Si ; calc. 316.1607).
2-Methylprop-2-enyl Diazo(triethylsilyl)acetate (8c) [17][19]. From methallyl diazoacetate after FC (SiO2,
pentane/AcOEt 96 :4): yield 85%. Yellow oil. IR (film): 2953w, 2874w, 2114s, 2084s, 1684s, 1259m. 1H-NMR
(500 MHz, CDCl3): 0.76 (q, J ˆ 7.4, 6 H); 0.99 (t, J ˆ 7.4, 9 H); 1.77 (s, 3 H); 4.56 (s, 2 H); 4.95 (d, J ˆ 23.0, 2 H).
‡
13C-NMR (125 MHz, CDCl3): 3.0 (t); 7.0 (q); 19.4 (q); 67.9 (t); 112.7 (t); 140.1 (s); 169.2 (s). MS: 254 (3, M ),
‡
217 (68), 189 (49), 157 (48), 115 (55), 87 (100), 55 (62). HR-MS: 254.1471 (C12H22O2N2Si ; calc. 254.1450).
(2Z)-Pent-2-enyl Diazo(triethylsilyl)acetate (8d) [19]. From (2Z)-pent-2-enyl diazoacetate (7d) after FC
(SiO2, pentane/AcOEt 95 :5): yield 80%. Yellow oil. IR (film): 2954w, 2085s, 1687s, 1257s, 1074m. 1H-NMR
(500 MHz, CDCl3): 0.75 (q, J ˆ 7.8, 6 H); 0.98 (t, J ˆ 7.7, 9 H); 0.97 1.01 (m, 3 H); 2.12 (dquint., J ˆ 7.4, 1.4,
2 H); 4.68 (td, J ˆ 0.6, 6.9, 2 H); 5.48 5.53 (m, 1H); 5.61 5.67 ( m, 1 H). 13C-NMR (125 MHz, CDCl3): 3.1( t);
‡
7.0 (q); 14.0 (q); 20.9 (t); 60.4 (t); 122.9 (d); 136.8 (d); 169.5 (s). MS: 268 (1, M ), 211 (17), 171 (66), 143 (15),
‡
115 (86), 103 (70), 87 (100), 75 (33), 69 (51), 59 (37). HR-MS: 268.1623 (C13H24O2N2Si ; calc. 268.1607).
3.3. Intramolecular Cyclopropanation of Allyl Diazo(triethylsilyl)acetates 8a d. General Procedure. To the
RhII catalyst (2% with respect to 8) was added the diazosilylacetate 8a d (0.40 mmol) under Ar in 5 min. The
mixture was stirred during 2 h at r.t. The soln. was evaporated and the residue purified by FC.
(1S,5R)-1-(Triethylsilyl)-3-oxabicyclo[3.1.0]hexan-2-one (9a). FC (SiO2, pentane/AcOEt 97:3) afforded
9a. For yields, see Table 2. Colorless oil. Enantiomer separation by GC (Lipodex E, 5 min at 1208, then 18/min to
1608, 10 min at 1608): tR 17.3 ((1S,5R), major) and 18.4 ((1R,5S), minor); for abs. configuration, see below.
[a]2D0 ˆ ‡7.2 (c ˆ 1.00, EtOH; for 30% ee). IR (film): 2954m, 2876m, 1753s, 1248m, 994s. 1H-NMR (300 MHz,

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Helvetica Chimica Acta Vol. 87 (2004)
CDCl3): 0.59 0.67 (m, 6 H); 0.96 (t, J ˆ 8.1, 9 H); 1.17 (dd, J ˆ 7.0, 4.5, 1H); 2.04 2.06 ( m, 1H); 4.24 ( m, 2 H).
13C-NMR (MHz, CDCl3): 2.0 (t); 7.2 (q); 13.3 (s); 15.6 (t); 21.9 (t); 68.2 (t); 178.8 (s). MS: 183 (85,
‡
‡
[M À C2H5] ), 139 (30), 111 (100), 83 (42), 59 (27), 53 (36). HR-MS: 183.0850 (C9H15O2Si ; calc. 183.0841).
rel-(1R,5S,6R)-6-Phenyl-1-(triethylsilyl)-3-oxabicyclo[3.1.0]hexan-2-one (9b). After FC (SiO2, pentane/
AcOEt 97:3), yield 9% with [Rh2{(S)-nttl}4] and 10% with [Rh2{(S)-bpttl}4] (Table 3). Colorless oil. IR (film):
2953m, 2874m, 1713s, 1189s, 1051s, 966s. 1H-NMR (300 MHz, CDCl3): 0.31 0.52 ( m, 6 H); 0.88 (t, J ˆ 7.9, 9 H);
2.56 (d, J ˆ 4.5, 1H); 2.75 ( t, J ˆ 4.0, 1H); 4.40 4.50 ( m, 2 H); 7.30 7.40 (m, 5 H). 13C-NMR (75 MHz,
CDCl3): 2.9 (t); 7.3 (q); 23.6 (s); 25.7 (d); 33.3 (d); 68.3 (t); 127.7 (d); 128.4 (d); 129.2 (d); 135.2 (s); 178.4 (s).
‡
‡
MS: 259 (100, [M À C2H5] ), 157 (43), 129 (48), 115 (14), 87 (41), 59 (26). HR-MS: 259.1143 (C9H15O2Si ; calc.
259.1154).
rel-(1S,5R)-5-Methyl-1-(triethylsilyl)-3-oxabicyclo[3.1.0]hexan-2-one (9c). After FC (SiO2, pentane/
AcOEt 97 :3), yield 20% with [Rh2{(S)-nttl}4] (Table 3). Colorless oil. Enantiomer separation by GC (b-
Dex, 5 min at 1208, then 18/min to 1808, 10 min at 1808): tR 27.5 (minor) and 27.7 (major). IR: 2954m, 2879m,
1
1750s, 1188s, 1056s, 1006s. H-NMR (300 MHz, CDCl3): 0.68 0.76 (m, 6 H); 0.99 (t, J ˆ 7.5, 9 H); 1.09 (d, J ˆ
4.2, 1H); 1.16 ( d, J ˆ 3.9, 1H); 1.36 ( s, 3 H); 3.94 (d, J ˆ 8.8, 1H); 4.20 ( d, J ˆ 8.8, 1H). 13C-NMR (75 MHz,
‡
CDCl3): 2.5 (t); 7.3 (q); 16.8 (q); 22.9 (t); 30.0 (s); 72.2 (t); 113.9 (s); 179.4 (s). MS: 197 (100, [M À C2H5] ), 125
‡
(92), 115 (36), 103 (24), 97 (54), 87 (52). HR-MS: 197.1004 (C12H22O2Si ; calc. 197.0998).
cis-4-(1-Methylethenyl)-3-(triethylsilyl)oxetan-2-one (11). After FC (SiO2, pentane/AcOEt 97:3), yield
1
18% with [Rh2{(S)-nttl}4]. IR (film): 2956m, 2874m, 1807s, 1255w, 1111s, 1008s. H-NMR (300 MHz, CDCl3):
0.67 0.76 (m, 6 H); 0.98 (t, J ˆ 8.1, 9 H); 1.79 (s, 3 H); 3.55 (dd, J ˆ 6.4, 2.5, 1H); 4.88 ( d, J ˆ 6.4, 1H); 5.08
(s, 1H); 5.26 ( s, 1 H). 13C-NMR (75 MHz, CDCl3): 3.5 (t); 7.2 (q); 19.1 (d); 44.6 (q); 73.3 (d); 113.0 (t); 140.2
‡
(s); 170.0 (s). MS: 226 (3, M ), 198 (17), 197 (100), 125 (54), 103 (38), 75 (54). HR-MS: 226.138750
‡
(C12H22O2Si ; calc. 226.1389).
(1S,5R,6R)-6-Ethyl-1-(triethylsilyl)-3-oxabicyclo[3.1.0]hexan-2-one (9d). After FC (SiO2, pentane/AcOEt
97:3), yield 76% with [Rh2{(S)-nttl}4], 38% ee (determined after desilylation to 10d). For abs. configuration,
1
see below. Colorless oil. IR (film): 2952m, 2873m, 1745s, 1197w, 1070m, 1000m. H-NMR (500 MHz, CDCl3):
0.64 (q, J ˆ 7.7, 6 H); 0.96 (t, J ˆ 7.7, 9 H); 1.04 (t, J ˆ 7.2, 3 H); 1.26 1.55 (m, 3 H); 2.08 (t, J ˆ 5.6, 1H); 4.13
(d, J ˆ 9.6, 1H); 4.29 ( dd, J ˆ 9.6, 5.5, 1H). 13C-NMR (MHz, CDCl3): 2.1( t); 7.2 (q); 13.3 (q); 17.0 (t); 19.4 (s);
‡
27.1( d); 27.3 (d); 65.1( t); 177.1 (s). MS: 211 (100, [M À C2H5] ), 115 (16), 109 (15), 103 (69), 81 (25), 75 (46).
‡
HR-MS: 211.1158 (C11H19O2Si ; calc. 211.1154).
3.4. Desilylation of 1-(Triethylsilyl)-3-oxabicyclo[3.1.0]hexan-2-ones 9a,d: General Procedure. At r.t., 1m
Bu4NF in THF (1ml) was added dropwise to the appropriate oxabicyclohexanone (0.56 mmol). After stirring
for 2 4 h, H2O (2.0 ml) was added, the mixture extracted with CH2Cl2, the org. layer dried (MgSO4) and
evaporated, and the residue purified by FC.
(1R,5S)-3-Oxabicyclo[3.1.0]hexan-2-one (10a). FC (SiO2, pentane/AcOEt 96 :4) afforded 12 mg (36%) of
10a. Colorless oil. Enantiomer separation by GC (Lipodex E, 10 min at 1008, then 18/min to 1508, 10 min at
1508). tR 27.6 ((1R,5S), major) and 29.8 ((1S,5R), minor); for abs. configuration, see 3.4. 1H-NMR (300 MHz,
CDCl3): 0.85 0.88 (m, 1H); 1.22 1.30 ( m, 1H); 2.03 2.10 ( m, 1H); 2.20 2.27 ( m, 1H); 4.22 ( d, J ˆ 9.2 Hz,
1H); 4.32 4.37 ( m, 1 H).
(1R,5S,6R)-6-Ethyl-3-oxabicyclo[3.1.0]hexan-2-one (10d). FC (SiO2, pentane/AcOEt 96 :4) afforded
12 mg (37%) of 10d. Colorless oil. Enantiomer separation by GC (Lipodex E, 5 min 1208, 18/min to 1608, 10 min
1608): tR 17.4 ((1S,5R,6S), minor) and 18.1 ((1R,5S,6R), major); for abs. configuration, see 3.4. [a]2D0 ˆ 26.3 (c ˆ
0.24, EtOH, for 28% ee). IR (film): 2965m, 2876w, 1756s, 1173w, 1058s, 979s. 1H-NMR (300 MHz, CDCl3): 1.07
(t, J ˆ 6.8, 3 H); 1.40 1.43 (m, 3 H); 2.18 2.29 (m, 2 H); 4.15 (d, J ˆ 9.9, 1H); 4.41 ( dd, J ˆ 9.8, 5.3, 1H).
‡
13C-NMR (75 MHz, CDCl3): 13.3 (q); 16.3 (t); 22.5 (d); 22.7 (d); 23.9 (d); 66.0 (t); 175.1 (s). MS: 126 (3, M ),
‡
111 (9), 97 (15), 85 (100), 67 (84), 55 (46). HR-MS: 126.0688 (C7H10O2 ; calc. 126.0680).
3.4. Absolute Configuration of 10a,d. Optically active 3-oxabicyclo[3.1.0]hexan-2-ones 10a,d of known
absolute configuration were synthesized via intramolecular cyclopropanation of 7a and 7d, respectively, in the
presence of [Rh2{(S)-mepy}4] according to the General Procedure described in 3.3.
(1R,5S)-3-Oxabicyclo[3.1.0]hexan-2-one (10a). FC (SiO2, pentane/AcOEt 95 :5) afforded 61mg (37%) of
10a with 89% ee. Enantiomer separation by GC (Lipodex E, 10 min at 1008, then 18/min to 1508, 10 min at 1508):
tR 27.0 ((1R,5S), major) and 29.9 ((1S,5R), minor).
(1R,5S,6R)-6-Ethyl-3-oxabicyclo[3.1.0]hexan-2-one (10d). FC (SiO2, pentane/AcOEt 95 :5) gave 46 mg
(38%) of 10d with 97% ee. Enantiomer separation by GC (Lipodex E, 5 min at 1208, then 18/min to 1608, 10 min
at 1608): tR 17.3 ((1S,5R,6S), minor) and 17.9 ((1R,5S,6R), major).

Helvetica Chimica Acta Vol. 87 (2004)
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REFERENCES
[1] H. Tomioka, in − Houben-Weyl, Methoden der Organischen Chemie×, Vol. E 19b, Teil 2, Ed.; M. Regitz,
Thieme Verlag: Stuttgart, 1989, p. 1431 1446.
[2] U. Schˆllkopf, N. Rieber, Angew. Chem., Int. Ed. 1967, 6, 884; U. Schˆllkopf, D. Hoppe, N. Rieber, V.
Jacobi, Liebigs Ann. Chem. 1969, 730, 1 .
[3] G. Maas, M. Alt, D. Mayer, U. Bergstr‰saser, S. Sklenak, P. Xavier, Y. Apeloig, Organometallics 2001, 20,
4607.
[4] G. Maas, M. Gimmy, M. Alt, Organometallics 1992, 11, 3813.
[5] S. P. Marsden, W. K.Pang, Tetrahedron Lett. 1998, 39, 6077; S. N. Kablean, S. P. Marsden, A. M. Craig,
Tetrahedron Lett. 1998, 39, 5109.
[6] S. P. Marsden, W.-K. Pang, Chem. Commun. 1999, 1199.
[7] C. Bolm, A. Kasyan, K. Drauz, K. G¸nther, G. Raabe, Angew. Chem., Int. Ed. 2000, 39, 2288.
[8] P. M¸ller, F. Lacrampe, G. Bernardinelli, Tetrahedron: Asymmetry 2003, 14, 1503.
[9] S. Hashimoto, N. Watanabe, S. Ikegami, Tetrahedron Lett. 1990, 31, 5173.
[10] S. Kitagaki, M. Anada, O. Kataoka, K. Matsuno, C. Umeda, N. Watanabe, S. Hashimoto, J. Am. Chem. Soc.
1999, 121, 1 41 7.
[11] a) M. P. Doyle, Aldrichim. Acta 1996, 29, 3; M. P. Doyle, M. A. McKervey, T. Ye, −Modern Catalytic
Methods for Organic Synthesis with Diazo Compounds×, Wiley-Interscience, New York, 1998, p. 112 162;
b) H. M. L. Davies, Aldrichim. Acta 1997, 30, 105; H. L. M. Davies, Eur. J. Org. Chem. 1999, 2459; c) M. P.
Doyle, W. Hu, ARKIVOC 2003, VII, 15; M. P. Doyle, S. B. Davies, W. Hu, Org. Lett. 2000, 2, 1145.
[12] J. Wolinski, F. Muzalewski, G. Kupryszewski, Matematyka, Fizyka, Chemia 1968, 8, 177.
[13] T. Allspach, H. G¸mbel, M. Regitz, J. Org. Chem. 1985, 290, 33.
[14] G. Maas, T. Werle, M. Alt, D. Mayer, Tetrahedron 1993, 49, 881.
[15] D. A. Evans, K. A. Woerpel, M. M. Hinman, M. M. Faul, J. Am. Chem. Soc. 1991, 113, 726.
[16] J. K. Crandall, T. Schuster, J. Org. Chem. 1990, 55, 1973.
[17] M. P. Doyle, R. E. Austin, A. S. Bailey, M. P. Dwyer, A. B. Dyatkin, A. V. Kalinin, M. M. Kwan, S. Liraqs,
C. J. Oalman, R. J. Pieters, M. N. Protopopova, C. E. Raab, G. H. P. Roos, Q. Zjou, S. F. Martin, J. Am.
Chem. Soc. 1995, 117, 5763.
[18] P. M¸ller, P. Polleux, Helv. Chim. Acta 1994, 77, 645.
[19] F. Lacrampe, Ph.D. Thesis, No. 3512, University of Geneva, 2004.
[20] T. Allspach, H. G¸mpel, M. Regitz, J. Organomet. Chem. 1985, 290, 33.
[21] D. J. Adams, A. J. Blake, P. A. Cooke, C. D. Gill, N. S. Simpkins, Tetrahedron 2002, 58, 4603.
¬
¬
[22] P. Lahuerta, I. Pereira, J. Perez-Prieto, M. Sanau, S. Stiriba, D. F. Taber, J. Organomet. Chem. 2000, 612, 36.
[23] H. G¸nther, −NMR Spektroskopie×, Thieme Verlag, Stuttgart, 1973.
[24] Y. Takekama, K. Shishido, J. Org. Chem. 2001, 66, 8490.
[25] P. M¸ller, P. Nury, Helv. Chim. Acta 2001, 84, 662.
[26] M. P. Doyle, W. R. Winchester, M. N. Propopotova, A. P. Kazala, L. J. Westrum, Org. Synth. 1995, 73, 1 3.
[27] M. P. Doyle, W. R. Winchester, J. A. A. Hoorn, V. Lynch, S. H. Simonsen, R. Ghosh, J. Am. Chem. Soc.
1995, 73, 9968.
[28] M. Kennedy, M. A. McKervey, A. M. Maguire, G. H. P. Roos, J. Chem. Soc. Chem. Commun. 1990, 361.
[29] H. M. L. Davies, P. R. Bruzinski, D. H. Lake, N. Kong, M. J. Faul, J. Am. Chem. Soc. 1996, 118, 6897.
[30] P. M¸ller, Y. Allenbach, E. Robert, Tetrahedron: Asymmetry 2003, 14, 779.
[31] C. S. Wilcox, R. E. Babston, Synthesis 1985, 941.
[32] W. Kirmse, Chem. Ber. 1965, 98, 4027; M. Alt. G. Maas, Chem. Ber. 1994, 127, 1537; M. P. Doyle, R. J.
Pieters, S. F. Martin, R. E. Austin, C. J. Oalman, P. M¸ller, J. Am. Chem. Soc. 1991, 113, 1423.
[33] Y. Takekama, K. Shishido, J. Org. Chem. 2001, 66, 8490.
Received July 31, 2004